Ultrasensitive DNA Detection based on Inorganic-Organic Nanocomposites Cosensitization and G-quadruplex/hemin Catalysis for Signal Amplification.

A novel photoelectrochemical (PEC) aptasensor was fabricated for DNA detection based on the coupling of cosensitization and peroxidase-like catalytic activity. Specifically, the surface of branched-TiO2 nanorods (B-TiO2 NRs) was modified with Cd2+ and S2+ to obtain B-TiO2 NRs/CdS hybrid structures, which was subsequently used as a matrix to immobilize hairpin DNA (hDNA) probe. CdTe/TCPP (TCPP = meso-tetra(4-carboxyphenyl)-porphine) used for signal amplification was labeled on the terminal of hDNA probe. Without target DNA (tDNA) presence, the immobilized hDNA probe with CdTe/TCPP possessed hairpin form and was located near the B-TiO2 NRs/CdS electrode surface, forming a cosensitized structure formation and then generating strong photocurrent with H2O2 as the electron donor. During detection, the specific recognition of tDNA by the sensing hDNA probe triggered the formation of the G-quadruplex/hemin DNAzyme, which would effectively catalyze the decomposition of H2O2. Meanwhile, cosensitization would disappear when hDNA probe hybridized with tDNA, further reducing the photocurrent. With double signal amplification strategy, the sensing platform designed in this work demonstrated linear detection ability in the 0.5 fM-5 nM range with detection limit equal to 0.14 fM. Notably, through encoding in the base sequences of the hDNA and marking it, a versatile PEC platform could be structured for the detection of various DNA targets, which could promise applications in point-of-care diagnostic fields.